We routinely etch 50 to 75u silicon in production using a 2:1:1
(Nitric,HF, Acetic) etch at
6'C with SC450 resist as the mask with or without underlying oxide. The
resist is a negative
tone resist made by Arch.
The resist etch rate is 0.

Contact me if you need further details.

avi

Avi Laker
Teccor Electronics
972 756 8237   Office
214 439 6770   Pager